Several methods have been used in the past for removing carbon monoxide and other gaseous materials from mixtures of gases. Copper salts, e.g., cuprous chloride, have been used as early as 1850 to dissolve carbon monoxide. Another method, called the "Cosorb" process, generally has involved contacting a hydrocarbon stream with a cuprous tetrachloroaluminate toluene complex in a toluene solution. Still another method, sometimes called the "copper-liquor" process, has involved contacting a hydrocarbon stream with an aqueous copper ammonium salt solution.
These past methods unfortunately have suffered from various shortcomings. Cuprous chloride, for example, generally requires a highly corrosive environment. The Cosorb process is typically unable to handle even relatively small amounts of water, so that, in a continuous process, an additional step is often required to minimize or remove water from the gas stream being treated. Finally, aqueous copper ammonium salt solutions are relatively corrosive and unstable.